I. Field of the Invention
The present invention relates to a process and apparatus for removing ammonia-containing compounds from aqueous fluids and process streams such as water. More particularly, the present invention relates to a process and apparatus whereby contaminated water is successfully treated to remove ammonia-containing compounds. Even more particularly, the present invention provides a process and apparatus which permits the chemical treatment of ammonia-containing compounds so removed to yield environmentally neutral reaction products.
II. Description of the Prior Art
As a result of growing concern for the purity of water resources and, in response to growing governmental pressures to maintain the quality of these water resources, industry and other large-scale water consumers have been required to investigate and implement methods for reducing various chemical pollutants discharged in their effluent streams. Ammonia-containing compounds are employed in a variety of manufacturing processes such as the production of zeolite catalysts. In the manufacture of such cracking catalysts, sodium ions are removed by washing the catalytic material with a solution containing ammonium sulphate. This process results in large volumes of waste water which are contaminated with various salts including ammonium sulphate.
Various methods have been proposed, discussed and employed to remove ammonia-containing contaminants such as ammonium sulphate from effluent stream. The most common methods employ aqueous sodium hydroxide to raise pH of the effluent stream to a level above 9. At this pH level, gaseous ammonia is liberated from the aqueous stream and can be vented or recovered as required. This process generally removes gross amounts of ammonia. However large concentrations of ammonia-containing compounds can still remain in the effluent stream.
In recent years, ammonia recovery has become an environmental necessity. Growing concern for water and air quality have resulted in stricter governmentally enforced standards regarding the manner and quantity of the ammonia discharge. It is anticipated that in the near future, governmental agencies such as the United States Environmental Protection Agency will require water discharge streams to contain no more than 10 ppm, or that amount which will permit the survival of 3 out of 5 minnows in water containing the ammonia or ammonia-containing compounds.
A variety of recovery systems have been employed in an effort to comply with governmental mandates regarding environmental pollution. In recent years, the cost of raw materials necessary to implement such recovery has risen sharply. While this adversely affects the economic viability of such ammonia recovery processes, increasing environmental concerns make it imperative that ammonia and ammonia-containing compounds be removed from waste water steams even at extraordinarily high economic costs. These high economic costs will, necessarily, be passed back to consumers of products which require the generation of waste ammonia or ammonia-containing contaminants. This will make such domestic processes non-competitive with processes occurring in countries which disregard the adverse impact of pollution on their respective local environments. Consequently, a variety of alternative processes have been proposed.
One example of ammonia-recovery processes is disclosed in U.S. Pat. No. 1,266,147 to Ore. The Ore process employs lime in the recovery of ammonia from cold distillation streams. In the Ore process, lime is added to the process water containing ammonia at temperatures between about 44.degree. C. and about 70.degree. C. to liberate ammonia in gaseous form. The Ore process makes no provision for the efficient collection of generated ammonia and is silent on a method for removing the final trace amounts of ammonia present after gaseous liberation.
U.S. Pat. No. 4,093,544 to Ross describes a method and apparatus for removing ammonia and other nitrogen containing compounds from waste water by increasing the pH of the water with an alkaline agent such as lime. The Ross reference creates additional pollution problems in that it fails to address the problem of calcium contamination in the process stream.
A number of ammonia removal processes have been proposed which involve aqueous distillation procedures. In such procedures, a caustic material such as lime is added to the process stream to raise the pH during distillation. The resulting water vapor and gaseous ammonia evolved during distillation are removed while the unwanted calcium-salts remain in the distillation chamber. Theoretically only small amounts of the calcium salts are carried with the distilled material to subsequent ammonia stripping chambers. Such processes are extremely energy intensive and do not address problems related to removal of dissolved solids which result from such procedures and the disposal of materials such as lime added during the various processes to facilitate ammonia removal. Some examples of these processes include U.S. Pat. Nos. 1,936,864 and 1,983,320 to Spur, Jr.; U.S. Pat. No. 2,018,863 to Miller; and U.S. Pat. No. 4,140,131 to Didycz et al.
None of the processes discussed addresses the difficulties encountered in removing the final trace amounts of ammonia remaining in an effluent stream after ammonia stripping or other waste water treatment. Trace amounts of ammonia or ammonia-containing compounds in aqueous effluent as low as 10 ppm have been found to have deleterious effects on the ecosystems of lakes and streams to which they are discharged. In recognition of this the US EPA has issued more stringent restrictions on the ammonia content of aqueous effluent to the result that discharge streams be capable of supporting aquatic life so that no more than two minnows out of five die when exposed to the discharge water. To meet these stricter standards, it is becoming necessary that discharge water streams be rendered essentially ammonia-free; a standard impossible to reach by employing water treatment processes such as those outlined previously.
Thus, it would be desirable to provide a process for reducing ammonia and ammonia-containing compounds in waste water to levels at or below those mandated by the appropriate environmental protection authorities which are fully capable of supporting and maintaining aquatic life. It is also desirable that this process and apparatus be an integrated self-contained system which would efficiently isolate and recover substantially all ammonia and ammonia-containing compounds removed during the water treatment process. It is also desirable that the process yield compounds which are subsequently useful or present in an environmentally neutral form. It is also desirable that the process and apparatus of the present invention be capable of continuous use as required. It is also desirable that the process provide the ability to regenerate any catalyst or purification compounds in situ without interfering with ongoing water purification.